Syringe-pusher devices according to the prior art generally employ an active means for translation of the piston of the syringe whose body is fixed on the apparatus.
Among such translation means, the one most often met with is a carriage and an endless screw actuated by an electric motor.
The motor which actuates the endless screw is either of the step-by-step or D.C. type. In the latter case, a reduction gear is generally placed between the motor and the endless screw.
For a geometrically defined syringe, the output of solution injected is directly proportional to the speed of translation of the piston-pusher member, said speed being in turn directly proportional to the angular rotation speed of the endless screw.
The angular speed of the endless screw may be adjusted in continuous rotation, for example by controlling the supply of the electric motor.
More recently, a discontinuous rotation of the endless screw has been preferred, by means of active periods separated by periods of relaxation. Elementary volumes or boluses are thus distributed during the active periods. A range of variation of the mean angular speed of the endless screw, and therefore of the mean output, which is much more extensive, for example from 1 to 100, is thereby obtained.
A programmer, generally a clock, initiates the rotation of the endless screw, which rotation terminates after description of a predetermined, constant angle.
A recent variant embodiment consists in replacing the programmation of the stop by a servo-control which stops the motor when the angle necessary and sufficient for delivering an elementary volume has been described. The variations in speed of the motor then have no influence on the volumetric precision of the elementary volume.
The output is adjusted by varying the frequency of the initiations of rotation of the endless screw, which is generally obtained by varying the duration of the relaxation insofar as the latter remains large compared with the duration of the active periods then considered as negligible.
These modes of adjustment of the speed of translation of the piston-pusher member present drawbacks.
In fact, the dosage generally being expressed in mols or units of active product per kilogram of body weight and per day, its translation into speed of translation of the piston of the syringe requires prior calculations. Generally, only one type of syringe can be used. Or it is necessary to employ conversion tables displaying the output as a function of the type of syringe used.
Moreover, the necessary durations of relaxation with low outputs obtained with syringes of too large relative capacity may be incompatible with the half-life of the drug injected and/or with the maintenance of the permeability of the intra-vascular injection means.
In addition, the time taken for the syringe to empty completely is variable, which renders the time table for renewing its content different from one patient to another.
Finally, the continuous operation of the motor is generally too slow to allow the rearward return of the carriage other than by disengaging said carriage and pushing it manually.
To make this type of syringe-pusher device, it may be constructed around a coaxial electro-mechanical assembly 1,2,3,4 contained in a closed envelope 5. Said electro-mechanical assembly 1,2,3,4 and the electronic control members 6 as well as the supply battery 7 may advantageously be placed in a casing 8 whose adequately formed expansions maintain the body of the syringe 9 by clamping, as in Patent PCT/FR87/00226 (FIG. 1).